A housing for a turbine used in a turbocharger and the like has a scroll part. This scroll part extends along the circumferential direction of a turbine rotor blade to surround the turbine rotor blade. The scroll part is configured so that fluid flowing into an inlet of the scroll part impinges on the turbine rotor uniformly over the entire circumference of the turbine blade. Specifically, the scroll part is configured such that a A/R ratio of a flow passage area A of the scroll part to a distance R between an axis of the turbine rotor blade and a flow passage center of the scroll part decreases from the inlet of the scroll part toward an end of the scroll part.
For instance, FIG. 4 of Patent Reference 1 illustrates curves representing respective relationships between a position of a passage of the scroll part in the circumferential direction of the turbine rotor and the A/R ratio. These curves have upward convex shapes, and a change rate of A/R increases on a terminal side of the scroll part.
Further, there are some cases where A/R linearly decreases from a turbine inlet to a turbine exducer.